I had a significantly-damaged frame repaired by Ruckus Composites in the past. The rebuilt frame was indistinguishable in ride quality and appearance from before it got damaged. Small repairs like your chain suck damage probably cost less than you expect, while larger tube repairs can get fairly expensive.
I was able to sell the bike later on at a fair price, essentially as an undamaged frame. Some buyers might not be ok with it, but be transparent about it. Since your repair would not be a major structural one, I do not see it being a major resale issue, especially in the current seller’s market.